Line Spacing

The only thing I can't get to work is line spacing. There has to be some way to change between single space, double space, etc. There are methods Spacing(), SpacingAfter(), SpacingBefore on the Paragraph class, but these don't appear to affect anything.

You should be able to use the following to set a Paragraph's LineSpacing to 1,5:

par.LineSpacing = 1.5f;

However, I found this changes the spacing between words rather than between lines. Unless I am mistaken, I would say Line Spacing means the distance between the lines of a paragraph, not the distance between the words in a paragraph.

If you want to change the distance between the lines of a paragraph, I just uploaded a patch that enables you to do so using the method SetLineSpacing.
It can be used like this:

// Use the default type, Line, to set spacing between lines
par.SetLineSpacing(LineSpacingType.Line, 1.5f);
// Use one argument to set the spacing to Auto. Can be used to set Before, After and both using Auto
par.SetLineSpacing(LineSpacingTypeAuto.AutoBefore);
// Use the type None to remove spacing
par.SetLineSpacing(LineSpacingTypeAuto.None);

The patch has already been applied to the latest source code. You can download the source code and build your own dll from there.

Or, if you already have a project based on the DocX source code, you could
download the patch . You can either simply copy the code into the Paragraph.cs file (though I think you might have to remove some +'s) or you could use TortoiseSVN (which I used to create the patch) to apply the patch.

Might be there are more ways to accomplish this, I'm only familiar with these options.

par.SetLineSpacing(LineSpacingType.Line, dSPacing)
//Instead of par.LineSpacing = dSPacing | LineSpacingType can also be After or Before

I didn't edit the original method of setting the LineSpacing value directly. I don't get an error when I use .LineSpacing though, for me it sets the spacing between letters rather than the spacing between lines.

I suspect the "Unexpected error" might be caused by something else (if changing the lines above doesn't help). Could you provide the XML from line 10 of your document.xml file, if you're still getting the error? (Perhaps just the part that's giving
the error, around column 3198.)

At the top of the CodePlex page, there's a "Source Code" tab, at the "Source Code" screen you'll find a "Download" button where you can download the DocX project.
Then open the downloaded project and compile it into your own DocX.dll to reference in your project. Alternatively, you could add the DocX project to your own solution and referende that project.